During the operation of a AG or SAG mills, the ore is ground in the milling chamber, where when reaching the desired size, passes along with the water for the process, through the slots in the discharge grate which is part of the discharge cover. Once the material crosses through the grate, its build-up in the pulp lifter, flowing while the mill rotates toward the discharge cone located in the middle position of the discharge cover where it exhausts the mill. The design of the pulp lifter and/or the discharge cone can produce the excessive clogging in the flow of the material exiting the mill or the greater size particles might obstruct the exit. In both cases, the flow of the discharge decreases, the material remains in the pulp lifter and the material that can exit from the inside of the mill can not do so, thus producing overload in the equipment, decreasing the processing capacity of the mill and generating significant production losses. Generally it is not possible to clearly identify these deficiencies during the process whereas the mill operator modifies the operational variables until partially or totally resolving the issue. In some cases, the solution is not achieved by modifying the operational variables, being possible to identify the issue only through stopping the mill, which leads to greater production losses.
This is the reason there is a need for some type of system allowing measuring the flow of material consistently discharged, in real time, as to determine what is happening both inside the pulp lifter and the discharge cone as to monitor said flow. Information in such way obtained would allow the operator to have a new control variable as to address in the most effective manner the operational conditions producing a lower discharge flow from the mill or to identify what are the conditions in the design producing the conditions of operational loss (while these components meet their life cycle, they are subject to wearing by abrasion from contact with the flow of material going through thereof, thus modifying its design).
A number of attempts had been made in the state of the art aiming to provide real-time monitoring of the conditions under which the milling is being done while the mill is under operation. For example, in U.S. Pat. No. 6,874,364 (Campbell et al.) published on Apr. 5, 2005, discloses a system to monitor mechanical waves in a machine that has particles in motion when in operation, wherein the system includes at least a sensor located in the machine at a distal location from the central axis of the machine, and the sensors are designed to detect acoustic waves and include a transmitter to transmit signals representing the mechanical waves detected to a receiver located in a remote location from the sensor(s), a data processor connected to the receiver to receive signal from the receiver representing the mechanical waves and to process signals as to produce output signals for further visualization in a screen, where the output signals represent one or more parameters indicative of the mechanical waves produced by the machine during a specific period of time.
Document U.S. Pat. No. 5,698,797 (Fontanille et al.) published on Dec. 16, 1997, discloses a monitoring device for a ball mill which has a group of balls arranged, during the rotation of the mill at a normal speed, between two generators (lb, lb) separated to a minimum angle (α) and a maximum angle and a mass of coal arranged during the rotation of the mill at a normal speed between two generator (lc, lc) separated in an angle (β), and which consists of a wave transmitter, waves selected from between the electromagnetic waves, wherein said transmitter can be arranged within the mill, and receiver means for such waves, wherein said receiver means are connected to an electronic circuit to determine the parameters corresponding to the number of balls, the amount of coal, and the wearing of the cover, where such means can be arranged in the external part of the mill in such a way that they can detect the waves crossing a generator lb and the waves in the external part of the maximum angle sections and β, as to determine the wearing of the cover; and that they can detect the waves in the angle section β not common to the angle section in order to determine the amount of coal. The wave receiver means are arranged in a rotational manner around the longitudinal axis of the cover in an angle section above the angle section encompassing α and β. 3. In this system the transmitter is located in the longitudinal axis of the cover whereas such transmitter is a gamma-ray photon type transmitter. The electronic circuit to determine the number of balls include, for each generator (lb, lb), one converter and one lineariser, wherein the signals from each lineariser are associated as to calculate the number of balls. The electronic circuit to determine the wearing in the case consists of a converter connected to a device to read the degree of wearing.
Document DE 4215455 (Godler) published Nov. 18, 1993, discloses a system with sensors for sound signals produced as a response to the noise generated by the milling plant, signals that are then analyzed as to render a measurement value of the status of operation of the plant. The status of the operation is measured as per the level of the mill. In order to analyse the noise, the system creates a noise spectrum and includes a device for a fast Fourier transformation. It also includes a device that creates the average of the spectrum during a long period of time. This system allows determining the performance of the mill, particularly a mill for rocks, in order to improve it and to improve the quality of the processed material.
The three documents described above disclose methods and apparatus that detect noise and make the correlation of said noise as to determine some of the operation properties. However, none of these teaches how to consistently measure the flow, in real time, as to determine what is happening both inside the pulp lifter and the discharge cone as to monitor said flow.